A polarizing plate having a desired extinction ratio in a visible light region and light resistance against intense light, and a liquid crystal projector using the above polarizing plate are provided. A polarizing element includes a substrate transparent to visible light, and inorganic particle layers in each of which inorganic particles are linearly disposed, the inorganic particle layers being disposed on the substrate at predetermined intervals to form a wire grid structure, the inorganic particles each have an elliptical shape having a major axis of the inorganic particles in the disposed direction and minor axis in a direction perpendicular thereto.
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0. 12. A polarizing element comprising:
a substrate;
a plurality of reflection layers provided on the substrate, the plurality of reflection layers extend in a first direction perpendicular to the substrate;
a dielectric layer provided on at least a portion of at least one of the plurality of reflection layers, the dielectric layer includes a dielectric layer material selected from the group consisting of SiO2, Al2O3, MgF2 and combinations thereof; and
a first inorganic particle layer including a plurality of first inorganic particles,
wherein the first inorganic particle layer is disposed on a top surface of the dielectric layer.
0. 33. A liquid crystal display comprising:
a liquid crystal panel;
a polarizing plate;
wherein the polarizing plate including:
a substrate;
a plurality of reflection layers provided on the substrate, the plurality of reflection layers extend in a first direction perpendicular to the substrate;
a dielectric layer provided on at least a portion of at least one of the plurality of reflection layers, the dielectric layer includes a dielectric layer material selected from the group consisting of SiO2, Al2O3, MgF2 and combinations thereof; and
a first inorganic particle layer including a plurality of first inorganic particles,
wherein the first inorganic particle layer is disposed on a top surface of the dielectric layer.
0. 26. A liquid crystal projector comprising:
a liquid crystal panel, an incident polarizing plate, and an emission polarizing plate;
wherein the emission polarizing plate including:
a substrate;
a plurality of reflection layers provided on the substrate, the plurality of reflection layers extend in a first direction perpendicular to the substrate;
a dielectric layer disposed on at least a portion of at least one of the plurality of reflection layers, the dielectric layer includes a dielectric layer material selected from the group consisting of SiO2, Al2O3, MgF2 and combinations thereof; and
a first inorganic particle layer including a plurality of first inorganic particles,
wherein the first inorganic particle layer is disposed on a top surface of the dielectric layer.
0. 1. A polarizing element comprising:
a first polarizing element including a first substrate transparent to visible light, and
first inorganic particle layers in each of which first inorganic particles are linearly disposed on the first substrate, the first inorganic particle layers being disposed on the first substrate at predetermined intervals to form a wire grid structure,
wherein the first inorganic particles each have an elliptical shape with a major axis in a disposed direction and a minor axis in a direction perpendicular thereto,
wherein the first polarizing element further includes convex portions, which are made of a material transparent to visible light and which extend in one direction, provided on the first substrate,
wherein the first inorganic particle layers are each provided on a top part or at least one of sidewall parts of each of the convex portions; and
a second polarizing element including a second substrate transparent to visible light, and
second inorganic particle layers in each of which second inorganic particles are linearly disposed on the second substrate, the second inorganic particle layers being disposed on the second substrate at predetermined intervals to form a wire grid structure,
wherein the second inorganic particles each have shape anisotropic properties in which a diameter in a disposed direction is long and a diameter in a direction perpendicular thereto is short,
wherein the second polarizing element further includes reflection layers of strip-shaped thin films, which are made of a metal and which extend in one direction, provided on the second substrate at predetermined intervals; and first dielectric layers provided on the reflection layers,
wherein the second inorganic particle layers are provided on the first dielectric layers at positions corresponding to those of the strip-shaped thin films, and
wherein the first and second substrates are adhered to each other at rear surfaces thereof.
0. 2. The polarizing element according to
wherein a refractive index of the first inorganic particles in the disposed direction is larger than that of the first inorganic particles in the direction perpendicular to the disposed direction.
0. 3. The polarizing element according to
wherein an extinction coefficient of the first inorganic particles in the disposed direction is larger than that of the first inorganic particles in the direction perpendicular thereto.
0. 4. The polarizing element according to
wherein the first inorganic particle layers are formed by an oblique sputtering method.
0. 5. The polarizing element according to
wherein the first inorganic particles include a single element selected from the groups consisting of: Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, and Sn, an alloy thereof, or a silicide semiconductor material.
0. 6. The polarizing element according to
wherein the first inorganic particles include a semiconductor material having a bandgap energy of 3.1 eV or less.
0. 7. The polarizing element according to
wherein the first inorganic particle layers have a thickness of 200 nm or less.
0. 8. The polarizing element according to
wherein the second substrate is processed by a rubbing treatment so that the direction of the rubbing treatment corresponds to the disposed direction of the first inorganic particles,
the polarizing element further comprising antireflection layers of inorganic particles having shape anisotropic properties, the antireflection layers being provided on the surface of the second substrate so that the direction of the inorganic particles corresponds to the disposed direction of the first inorganic particles.
0. 9. The polarizing element according to
further comprising
second dielectric layers, the second inorganic particle layers and the second dielectric layers forming laminates,
wherein at least one of the laminates is provided on each of the first inorganic particle layers.
0. 10. The polarizing element according to
0. 11. A liquid crystal projector comprising:
a lamp;
a liquid crystal panel; and
a polarizing element including a substrate transparent to visible light; and
first inorganic particle layers in each of which first inorganic particles are linearly disposed on the substrate, the first inorganic particle layers being disposed on the substrate at predetermined intervals to form a wire grid structure,
wherein the first inorganic particles each have an elliptical shape with a major axis in a disposed direction and a minor axis in a direction perpendicular thereto,
wherein the first polarizing element further includes convex portions, which are made of a material transparent to visible light and which extend in one direction, provided on the first substrate,
wherein the first inorganic particle layers are each provided on a top part or at least one of sidewall parts of each of the convex portions; and
a second polarizing element including a second substrate transparent to visible light, and
second inorganic particle layers in each of which second inorganic particles are linearly disposed on the second substrate, the second inorganic particle layers being disposed on the second substrate at predetermined intervals to form a wire grid structure,
wherein the second inorganic particles each have shape anisotropic properties in which a diameter in a disposed direction is long and a diameter in a direction perpendicular thereto is short,
wherein the second polarizing element further includes reflection layers of strip-shaped thin films, which are made of a metal and which extend in one direction, provided on the second substrate at predetermined intervals; and first dielectric layers provided on the reflection layers,
wherein the second inorganic particle layers are provided on the first dielectric layers at positions corresponding to those of the strip-shaped thin films, and
wherein the first and second substrates are adhered to each other at rear surfaces thereof.
0. 13. The polarizing element according to claim 12, further comprising a protective layer formed as an outermost surface of the polarizing element.
0. 14. The polarizing element according to claim 12, wherein the plurality of reflection layers include a strip-shaped thin film.
0. 15. The polarizing element according to claim 12, wherein the dielectric layer is formed over the substrate and includes a concave-convex shape having convex portions over the plurality of reflection layers and concave portions therebetween.
0. 16. The polarizing element according to claim 12, wherein the first inorganic particles include at least one of Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, Sn, an alloy thereof, and a silicide semiconductor material.
0. 17. The polarizing element according to claim 12, wherein the first inorganic particles include a semiconductor material having a bandgap energy of 3.1 eV or less.
0. 18. The polarizing element according to claim 12, wherein the first inorganic particle layer has a thickness of 200 nm or less.
0. 19. The polarizing element according to claim 12, wherein the polarizing element includes a wire grid structure.
0. 20. The polarizing element according to claim 12, wherein a first refractive index of the first inorganic particles in the first direction is smaller than a second refractive index of the first inorganic particles in a second direction perpendicular to the first direction.
0. 21. The polarizing element according to claim 20, wherein a first extinction coefficient of the first inorganic particles in the first direction is smaller than a second extinction coefficient of the first inorganic particles in the second direction.
0. 22. The polarizing element according to claim 12, wherein the substrate has a concave-convex member formed thereon, and the concave-convex member includes a pitch of 0.5 μm or less, a width of 0.25 μm or less, and a depth of 1 nm or more.
0. 23. The polarizing element according to claim 22, further comprising a second inorganic particle layer including a plurality of second inorganic particles, wherein the second inorganic particle layer is disposed on the concave-convex member.
0. 24. The polarizing element according to claim 12, further comprising antireflection layers being provided between the substrate and the reflection layers.
0. 25. The polarizing element according to claim 12, wherein the plurality of reflection layers spaced apart from each other at a predetermined interval on the substrate.
0. 27. The liquid crystal projector according to claim 26, wherein the emission polarizing plate includes an inorganic polarizing plate.
0. 28. The liquid crystal projector according to claim 26, wherein the dielectric layer is formed over the substrate and includes a concave-convex shape having convex portions over the plurality of reflection layers and concave portions therebetween.
0. 29. The liquid crystal projector according to claim 26, further comprising a protective layer formed as an outermost surface of the emission polarizing plate.
0. 30. The liquid crystal projector according to claim 26, wherein the first inorganic particles include at least one of Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, Sn, an alloy thereof, and a silicide semiconductor material.
0. 31. The liquid crystal projector according to claim 26, wherein the first inorganic particle layer has a thickness of 200 nm or less.
0. 32. The liquid crystal projector according to claim 26, wherein the plurality of reflection layers spaced apart from each other at a predetermined interval on the substrate.
0. 34. The liquid crystal display according to claim 33, wherein the dielectric layer is formed over the substrate and includes a concave-convex shape having convex portions over the plurality of reflection layers and concave portions therebetween.
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The present application is a continuation reissue application of Reissue application Ser. No. 13/912,572, filed on Jun. 7, 2013, which is an application for reissue of U.S. Pat. No. 7,957,062, filed as application Ser. No. 12/026,434 on Feb. 5, 2008, which claims priority to Japanese Patent Application Applications JP 2007-026348 and JP 2007-170585 filed in the Japanese Patent Office on Feb. 6, 2007 and Jun. 28, 2007, respectively, the entire contents of each of which are incorporated herein by reference.
The present application relates to a polarizing element having durability against intense light and a liquid crystal projector using the polarizing element.
In a liquid crystal display device, it is necessary to dispose at least one polarizing plate at a liquid crystal panel surface based on an image forming principle. The function of the polarizing plate is to absorb one of two polarized components (so-called P polarized wave and S polarized wave) perpendicular to each other and to transmit the other component. As the polarizing plate described above, a dichroic polarizing plate in the form of a film containing an iodine-based or a dye-based high molecular weight organic material has been frequently used in the past.
As a general method for manufacturing a dichroic polarizing plate, a method has been used having the steps of dyeing a polyvinyl alcohol-based film with a dichroic material, such as iodine, and then performing crosslinking using a crosslinking agent, followed by performing uniaxial drawing. Since being formed by the drawing as described above, this type of polarizing plate is liable to shrink. In addition, since a polyvinyl alcohol-based film is formed of a hydrophilic polymer, particularly under humidified conditions, the film is very liable to deform. In addition, since the film is used, the mechanical strength thereof is inevitably insufficient to be used as an element. In order to avoid the above problem, a method for using a transparent protective film may be used in some cases.
In recent years, liquid crystal display devices have been increasingly used in various applications, and the performances of the devices have also been improved. Concomitant with the trend described above, individual elements forming the liquid crystal display devices are requested to have high reliability and durability. For example, in a liquid crystal display device, such as a transmission type liquid crystal projector, using a light source having a large quantity of light, a polarizing plate receives intense radiation. Hence, the polarizing plate used in the above device as described above is requested to have superior heat resistance. However, since the film-based polarizing plate described above is formed of an organic material, improvement in properties thereof has been naturally limited to a certain level.
In order to solve the problem described above, an inorganic polarizing plate having superior heat resistance has been sold under the trade name “Polarcor” by Corning Inc., USA. This polarizing plate is formed of silver particles dispersed in glass and does not use an organic material such as a film, and the principle of this polarizing plate is to use plasma resonance of island-shaped particles. That is, light absorption caused by surface plasma resonance which occurs when light is incident on island-shaped particles of a noble metal or a transition metal is used, and an absorption wavelength is influenced by the particle shape and the dielectric constant of the surrounding material. When the island-shaped particle has an ellipsoid shape, since resonance wavelengths in the long-axis and the short-axis directions are different from each other, polarization properties are obtained thereby; in particular, a polarized component parallel with the long axis at a long wavelength side is absorbed, and a polarized component parallel with the short axis is transmitted. However, in the case of Polarcor, a wavelength region in which the polarization properties are obtained is a region in the vicinity of an infrared region, and a visible light region requested for liquid crystal display devices is not included. This is because of the physical properties of silver used for the island-shaped particles.
In U.S. Pat. No. 6,772,608, a UV polarizing plate formed by precipitating particles in glass by thermal reduction using the above principle has been disclosed, and as a particular example, silver used as metal particles has also been disclosed. In this case, it is believed that absorption in the short axis direction is used, which is different from the case of Polarcor described above. Although the polarizing plate functions at around 400 nm as shown in
In addition, in J. Opt. Soc. Am. A Vol. 8, No. 4, pp. 619 to 624, a theoretical analysis of an inorganic polarizing plate using plasma resonance of metal island-shaped particles has been disclosed. According to this document, it has been described that a resonance wavelength of aluminum particles is shorter than that of silver particles by approximately 200 nm, and hence when aluminum particles are used, a polarizing plate, which can be used in a visible light region, is probably manufactured.
In addition, in Japanese Unexamined Patent Application Publication No. 2000-147253, various methods for forming a polarizing plate using aluminum particles have been disclosed. Among the above methods, it has been disclosed that glass primarily formed of silicate is not preferable as a substrate since reaction occurs between the glass and aluminum, and calcium aluminoborate glass is suitably used (in paragraphs 0018 and 0019). However, glass formed of silicate has been widely commercially used as an optical glass, and highly reliable products thereof are available at a reasonable price; hence, when the glass formed of silicate is not suitably used, it is disadvantageous from an economical point of view. In addition, a method for forming island-shaped particles by etching using a resist pattern has also been disclosed (paragraphs 0037 and 0038). A polarizing plate used in a projector is generally requested to have a size of approximately several centimeters and a high extinction ratio. Accordingly, in order to form a visible-light polarizing plate, a resist pattern size is requested to be sufficiently smaller than a visible light wavelength, that is, to be several tens of nanometers, and in addition, in order to obtain a high extinction ratio, a pattern is preferably formed to have a high density. In addition, in order to use a polarizing plate for a projector purpose, a polarizing plate having a large area is desirably formed. However, as a method for forming a high density fine pattern by lithography, disclosed in this patent document, electron beam lithography is to be desirably used in order to obtain the pattern as described above. However, since the electron beam lithography is a method for drawing each pattern using electron beams, the productivity is inferior, and hence this technique is not practical.
In addition, in Japanese Unexamined Patent Application Publication No. 2001-147253, it has been disclosed that aluminum is removed by chlorine plasma; however, in general, when etching is performed as described above, chlorides adhere to sidewalls of an aluminum pattern. The chlorides may be removed by a commercially available wet etching liquid (such as SST-A2 by Tokyo Ohka Kogyo Co., Ltd.); however, since this type of chemical liquid, which reacts with aluminum chloride compounds, also reacts with aluminum although the etching rate is slow, it is difficult to realize a desired pattern shape by the method described above.
Furthermore, in Japanese Unexamined Patent Application Publication No. 2000-147253, as another method, a method has been disclosed in which aluminum is deposited on a patterned photoresist by oblique deposition, followed by removing the photoresist (paragraphs 0045 and 0047). However, it is believed that in order to ensure adhesion between a substrate and aluminum, aluminum is also preferably deposited on the substrate to a certain extent. However, it means that the shape of the aluminum film thus deposited is different from a prolate spheroid, such as a prolate ellipsoid, which is a suitable shape disclosed in paragraph 0015. In addition, in paragraph 0047, it has been disclosed that by anisotropic etching performed perpendicular to the surface, an excess deposit is removed. In order to obtain the function as the polarizing plate, shape anisotropic properties of aluminum are significantly important. Hence, it is believed important to adjust the amount of aluminum deposited on the resist portion and that on the substrate surface by etching to obtain a desired shape; however, it may be very difficult to control the amount of aluminum having a size of submicron or less, such as 0.05 μm, as disclosed in paragraph 0047, and hence it is questionable whether the method described above is a highly productive manufacturing method. In addition, as properties of the polarizing plate, a high transmittance is desirable in the transmission axis direction; however, when glass is used as the substrate, in general, several percentage of light is inevitably reflected on the glass interface, and since countermeasures have not been taken therefor, a high transmittance is difficult to obtain.
In addition, according to Japanese Unexamined Patent Application Publication No. 2002-372620, a polarizing plate formed by oblique deposition has been disclosed. This method is to obtain polarization properties by forming fine columnar structures by oblique deposition using a transparent and an opaque substance with respect to wavelengths in a service bandwidth, and since a fine pattern can be easily obtained by this method unlike the method disclosed in U.S. Pat. No. 6,772,608, it is believed that the method has a high productivity; however, problems still exist. That is, the aspect ratio of a fine columnar structure which is first formed from the substance opaque to the wavelengths in the service bandwidth, the distance between the fine columnar structures, and the linearity thereof are important factors to obtain superior polarization properties and are to be intentionally controlled in view of reproducibility of the properties. However, in this method, since the columnar structures are formed by a phenomenon in which initial deposited layers made of deposition particles form shadow areas, and following flying particles are not deposited on the shadow areas, it has been difficult to intentionally control the factors described above. As a method for improving the above situation, a method for forming polishing marks in the substrate by rubbing performed before deposition has been described; however, the particle diameter of the deposition film is approximately at most several tens of nanometers, and in order to control the anisotropic properties of this type of particles, it might be desired to intentionally form pitches on the order of submicron or less. However, by general polishing sheets or the like, pitches on the order of approximately submicron are the limit, and hence fine polishing marks as described above are difficult to form by rubbing. In addition, since the resonance wavelength of Al particles largely depends on the refractive index of the surrounding material, as described above, in this case, combination between the transparent and the opaque substances is important; however, in Japanese Unexamined Patent Application Publication No. 2002-372620, the combination to obtain superior polarization properties in a visible light region has not been described. In addition, as is the case disclosed in U.S. Pat. No. 6,772,608, when glass is generally used as the substrate, several percentage of light is inevitably reflected on the glass interface, and countermeasures have not been taken therefor.
In addition, in Applied Optics Vol. 25, No. 2, 1986, pp. 311 to 314, a polarizing plate for infrared communication, which is called Lamipol, has been described. This polarizing plate has a laminate structure of Al and SiO2, and according to this document, a very high extinction ratio is obtained. In addition, in J. Lightwave Tec. Vol. 15, No. 6, 1997, pp. 1042 to 1050, it has been disclosed that when Ge is used instead of Al which is responsible for the light absorption of Lamipol, a high extinction ratio can be realized at a wavelength of 1 μm or less. In addition, from
In U.S. Pat. No. 6,122,103, a wire grid type polarizing plate has been disclosed. This polarizing plate is formed from fine metal wires disposed on a substrate at a pitch smaller than the wavelength of light in a service bandwidth, and predetermined polarization properties are obtained by reflecting a polarized light component parallel with the fine metal wires and by transmitting a polarized light component perpendicular thereto.
In addition, in U.S. Pat. No. 6,813,077, a method has been disclosed in which a wire grid type polarizing element having a three-layered structure is formed by forming dielectric layers and metal layers on a metal lattice so as to cancels light reflected from the metal lattice by an interference effect, and in which a wire grid, which is generally a reflection type, is used as an absorption type. It is believed that when an absorption type polarizing plate is used by utilizing the optical properties obtained from a multilayer structure, as described above, the thickness and the optical properties of the metal layer formed on the dielectric layer are important; however, in this patent document, these important properties are not taken into consideration. That is, in this patent document, the above important properties have not been described, and hence the details have not been known; however, in order to obtain the interference effect as described above, light is necessary to pass through the metal layer. When light passes, it means that in this step, part of the light is absorbed in the metal film located at an upper side. By the absorption, the transmittance in the transmission axis direction is decreased, and this decrease is not preferable as the properties of the polarization transmission axis; in particular, it is not preferable for a liquid crystal display device which is requested to have a high transmittance in a visible light region. That is, a polarizing plate having an absorption effect does not function when the optical anisotropic properties of an absorption layer are not essentially controlled and is difficult to be used as a practical polarizing plate.
In addition, in Japanese Unexamined Patent Application Publication No. 2006-323119, an inorganic polarizing plate in which semiconductor nanorods are dispersed in glass has been disclosed. It has also been disclosed that superior polarization properties are obtained in a visible light region; however, since this polarizing plate is formed by a method similar to that for Polarcor of Corning Inc., a drawing step is inevitably performed, and as a result, a large size plate is difficult to obtain.
It is desirable to provide a polarizing plate, which has a desired extinction ratio in a visible light region and light resistance against intense light, and a liquid crystal display device using the above polarizing plate.
According to a first embodiment, there is provided a polarizing element comprising: a substrate transparent to visible light; and first inorganic particle layers in each of which first inorganic particles are linearly disposed on the substrate, the first inorganic particle layers being disposed on the substrate at predetermined intervals to form a wire grid structure, wherein the first inorganic particles each have an elliptical shape having a major axis in a disposed direction and a minor axis in a direction perpendicular thereto.
According to a second embodiment, as an optical constant of the first inorganic particle layers, an optical constant of the first inorganic particles in the disposed direction is preferably larger than that of the first inorganic particles in the direction perpendicular to the disposed direction.
In addition, according to a third embodiment, as the optical properties of the first inorganic particle layers, the refractive index of the first inorganic particles in the disposed direction is preferably larger than that of the first inorganic particles in the direction perpendicular thereto, and an extinction coefficient of the first inorganic particles in the disposed direction is preferably larger than that of the first inorganic particles in the direction perpendicular thereto.
In addition, according to a fourth embodiment, the first inorganic particle layers are preferably formed by an oblique sputtering method.
According to a fifth embodiment, the first inorganic particles preferably include a single element selected from Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, and Sn, an alloy thereof, or a silicide semiconductor material.
Alternatively, according to a sixth embodiment, the first inorganic particles preferably include a semiconductor material having a bandgap energy of 3.1 eV or less.
According to a seventh embodiment, the first inorganic particle layers preferably have a thickness of 200 nm or less.
In addition, according to an eighth embodiment, the polarizing element of the first embodiment may further comprise convex portions, which are made of a material transparent to visible light and which extend in one direction, provided on the substrate, and the first inorganic particle layers are each preferably provided on a top part or at least one of sidewall parts of each of the convex portions.
In addition, according to a ninth embodiment, the polarizing element of the first embodiment may further comprise reflection layers of strip-shaped thin films, which are made of a metal and which extend in one direction, provided on the substrate at predetermined intervals, and first dielectric layers provided on the reflection layers, and the first inorganic particle layers are preferably provided on the first dielectric layers at positions corresponding to those of the strip-shaped thin films.
According to a tenth embodiment, in the above ninth embodiment, the substrate is preferably processed by a rubbing treatment so that the direction of the rubbing treatment corresponds to the disposed direction of the first inorganic particles, and the polarizing element may further comprise antireflection layers of inorganic particles having shape anisotropic properties, the antireflection layers being provided on the surface of the substrate so that the direction of the inorganic particles corresponds to the disposed direction of the first inorganic particles.
According to an eleventh embodiment, the polarizing element according to the ninth embodiment may further comprise second inorganic particle layers in each of which second inorganic particles are linearly disposed; and second dielectric layers, the second inorganic particle layers and the second dielectric layers forming laminates, wherein at least one of the laminates is provided on each of the first inorganic particle layers.
According to a twelfth embodiment, there is provided a polarizing element comprising: the polarizing element according to the eighth embodiment; and the polarizing element according to the ninth embodiment, wherein the substrates thereof are adhered to each other at the rear surfaces thereof.
According to a thirteenth embodiment, the polarizing element described above may further comprise a polarizing element protective layer transparent to light in a service bandwidth as an outermost surface.
According to a fourteenth embodiment, there is provided a liquid crystal projector comprising: a lamp; a liquid crystal panel; and the polarizing element according to one of the first to the thirteenth embodiments.
The polarizing elements of the embodiments each have a desired extinction ratio in a visible light region and superior durability to that of a related polarizing element.
In addition, since the liquid crystal projector of the embodiment includes a polarizing element having superior light resistance against intense light, a highly reliable liquid crystal projector can be realized.
Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures.
The present application will be described below in greater detail with reference to the drawings according to an embodiment.
A polarizing element of an embodiment according comprises: a substrate transparent to visible light; and linear inorganic particle layers in which inorganic particles are continuously disposed on the substrate, the inorganic particle layers being disposed on the substrate at predetermined intervals to form a one-dimensional lattice wire grid structure, wherein the inorganic particles each have an elliptical shape having a major axis in the disposed direction and a minor axis in a direction perpendicular thereto. In addition, as an optical constant of the inorganic particle layers, an optical constant of the inorganic particles in the disposed direction is larger than that of the inorganic particles in the direction perpendicular thereto. In particular, the refractive index of the inorganic particles in the disposed direction is larger than that of the inorganic particles in the direction perpendicular thereto, and the extinction coefficient of the inorganic particles in the disposed direction is larger than that of the inorganic particles in the direction perpendicular thereto.
In the polarizing element of this embodiment, convex portions, which are formed of a material transparent to visible light and which extend in one direction parallel with a primary surface of the substrate, are provided on the substrate at predetermined intervals, and the inorganic particle layers are each formed on a top part or at least one of sidewall parts of each of the convex portions.
As shown in
The substrate 11 is formed of a material, such as glass, sapphire, or quartz, having a refractive index of 1.1 to 2.2 and being transparent to light (visible light region in this embodiment) in a service bandwidth. In this embodiment, glass, in particular, quartz (refractive index: 1.46) or soda-lime glass (refractive index: 1.51), is preferably used. A component composition of the glass material is not particularly limited, and for example, an inexpensive glass material, such as silicate glass which is widely used as an optical glass, may be used, so that manufacturing cost can be reduced. In addition, as the substrate 11, a quartz substrate or a sapphire substrate, having high thermal conductivity, is advantageously used in a polarizing element for an optical engine of a projector generating a large amount of heat.
A concave-convex member 14 is formed of the convex portions 14a having a rectangular cross-sectional shape, which are periodically provided on the primary surface of the substrate 11 to extend in one direction (absorption-axis Y direction) parallel with the primary surface of the substrate 11 at a predetermined pitch, which is smaller than a wavelength in a visible light region, in a direction (transmission-axis X direction) perpendicular to the absorption-axis Y direction of the substrate 11. In addition, the concave-convex member 14 is provided so that the inorganic particle layers 15 are to be formed thereon, and the wire grid structure of the inorganic particle layers is determined by the machined size and the pattern shape of the concave-convex member 14; hence, the concave-convex member 14 is important to obtain predetermined polarization properties of the polarizing element 10. That is, the machined size and the pattern shape of the concave-convex member 14 are appropriately determined in accordance with targeted polarization properties (extinction ratio) and/or an intended visible light wavelength region. In particular, in
In addition, the pitch, line width/pitch, concave portion depth (convex portion height), convex portion length, and top line width/bottom line width of the concave-convex member 14 are preferably set in the following ranges.
The concave-convex member 14 may be directly formed in the substrate 11 or may be separately formed. As a method for forming the concave-convex member 14, for example, there may be mentioned a lapping method using a polishing sheet; a method in which after a photoresist, which is used in semiconductor device manufacturing or the like, is applied on a substrate and is then patterned by exposure using a mask, the substrate is etched using the photoresist thus patterned as a mask; and a method in which by using a mold which is formed in accordance with dimensions of the concave-convex member 14, a mold shape is transferred on a substrate (nanoinprinting method), and an appropriate method may be selected among the above methods.
The convex portion 14a of the concave-convex member 14 may have a quadrangular, a trapezoidal, a sawtooth, or a triangular shape.
Since the inorganic particle layers 15 are each formed on the top part or at least one of the sidewall parts of each of the convex portions 14a, the inorganic particle layers 15, which are made of inorganic particles having shape anisotropic properties, each having a desired fine shape, can be disposed to form a stripe pattern on the surface of the substrate 11 and can be isolated from each other. In addition, since the concave-convex member 14 is mechanically formed, and the inorganic particle layers 15 are formed thereon, the concave-convex member 14 can be stably formed, and in addition, the shapes of the inorganic particle layers formed thereon can be easily controlled.
Since the inorganic particle layer 15 is formed by adhering inorganic particles to the top part or at least one sidewall part of the convex portion 14a, the inorganic particles are linearly disposed in one direction (absorption-axis Y direction) parallel with the primary surface of the substrate 11. “The inorganic particles are linearly disposed” indicates the state in which inorganic particles are connected to each other to form a strip-shaped continuous film or the state in which inorganic particles aggregate to form independent islands each having an appropriate size, and the islands are aligned in one direction to form a discontinuous film. As long as grain boundaries are formed, either one of the states described above may be used. In addition, since the inorganic particle layers 15 are formed on the convex portions 14a regularly provided at predetermined intervals, the inorganic particle layers 15 form a stripe pattern (one-dimensional lattice pattern), so that a wire grid structure is obtained.
In this embodiment, the inorganic particle has an elliptical shape having a major axis in the disposed direction and a minor axis in a direction perpendicular thereto. In addition, it is preferable that the inorganic particles have a size smaller than the wavelength in a service bandwidth and be completely isolated from each other.
In addition, as the optical constant of the inorganic particle layer 15 of this embodiment according to the present invention, it is important that the optical constant in the absorption-axis Y direction (disposed direction of the inorganic particles) be larger than that in the transmission-axis X direction (direction perpendicular to the disposed direction of the inorganic particles). In particular, the refractive index of the inorganic particle layer 15 in the absorption-axis Y direction is larger than that in the transmission-axis X direction, and the extinction coefficient of the inorganic particle layer 15 in the absorption-axis Y direction is larger than that in the transmission-axis X direction. In order to obtain the above properties, the inorganic particle layers 15 are formed by an oblique sputtering method.
The oblique sputtering deposition in order to form the inorganic particle layers 15 of this embodiment according to the present invention is shown in
In
As described above, when the incident direction of inorganic particles is controlled by inclining the substrate 11 with respect to the target 2 in deposition by a sputtering method, the inorganic particle layers 15 each selectively formed on the top part or at least one of sidewall parts of each of the convex portions 14a are obtained. In each of the inorganic particle layers 15, the inorganic particles are linearly disposed which have an elliptical shape having a major axis in the disposed direction and a minor axis in the direction perpendicular thereto, and in which the optical constant of the inorganic particle layer 15 in the absorption-axis Y direction is larger than that in the transmission-axis X direction.
In this embodiment, as a material (material forming inorganic particles) for the inorganic particle layer 15, a material appropriate as the polarizing element 10 is preferably to be selected in accordance with a service bandwidth. That is, a metal material and a semiconductor material are suitably used as the above material, and in particular, as the metal material, for example, there may be mentioned Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, Sn, or an alloy thereof. In addition, as the semiconductor material, for example, Si, Ge, Te, or ZnO may be mentioned. Furthermore, a silicide material, such as FeSi (in particular, β-FeSi2), MgSi2, NiSi2, BaSi2, CrSi2, or CoSi2, may also be preferably used.
In addition, when a semiconductor material is used for the inorganic particle layer 15, the absorption function relates to bandgap energy of the semiconductor. The reason for this is that light having energy equal to or less than the bandgap energy is absorbed. Hence, when a semiconductor material is used for a visible light polarizing element, the bandgap energy is necessary to be equal to or less than that of a service bandwidth. For example, in the case in which visible light is used, for absorption at a wavelength of 400 nm or more, a material having a bandgap energy of 3.1 eV or less is necessarily used. The bandgap energy also depends on the size of particles as described in OYO BUTURI, Vol. 73, No. 7, 2004, pp. 917 to 923, and in particular, when the size is decreased to several nanometers, the bandgap energy tends to rapidly increase; hence, in consideration of the size effect as described above, the material and the thickness thereof are to be appropriately determined. From the point as described above, a semiconductor material having a small bandgap energy in the bulk state is preferable, and for example, Ge is a preferable material for a visible light polarizing element since having a small bandgap energy of 0.67 eV (wavelength of approximately 1.85 μm) in the bulk state.
By the structure as described above, the polarizing element 10 has a desired extinction ratio in a visible light region and also has superior durability to that of a related polarizing element.
In addition, if desired, when the front and the rear surfaces of the substrate are coated with antireflection films, reflection at the interface between air and the substrate is prevented, and as a result, the transmission-axis transmittance can be improved. As the antireflection film, for example, there may be used a low refractive-index film of MgF2 or the like, which is generally used, or a multilayer film composed of a low refractive-index film and a high refractive-index film. In addition, after the structure shown in
Next, the structure of a polarizing element of a second embodiment.
In this embodiment, reflection layers in the form of strip-shaped thin films, which are made of a metal, which extend in one direction parallel with a primary surface of a substrate, and which are provided thereon with predetermined intervals, and dielectric layers formed on the reflection layers are provided, and the inorganic particle layers are formed on the dielectric layers at positions corresponding to those of the strip-shaped thin films.
As shown in
In this embodiment, the substrate 21 is formed from the same material as that for the substrate 11 of the first embodiment.
As the reflection layers 22, the strip-shaped thin films 22a, which are made of a metal and which extend in one direction (absorption-axis Y direction) parallel with the primary surface of the substrate 21, are provided thereon. As a material for the reflection layer 22, various materials may be used. For example, a metal, such as Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, or Te, or a semiconductor material may be used. In addition, besides the metal materials, for example, an inorganic film or a resin film, which has a high surface reflectance by coloring or the like, may also be used.
The thin films 22a are disposed on the surface of the substrate 21 with a pitch smaller than the wavelength of a visible light region and are formed (metal lattice), for example, by patterning of the above metal film using a photolithographic technique. The reflection layers 22 have a function as a wire grid type polarizer, and among various types of light incident on the surface of the substrate 21, a polarized wave (TE wave (S wave)) having an electric field component in a direction (Y-axis direction) parallel with the longitudinal direction of the wire grid is attenuated, and a polarized wave (TM wave (P wave)) having an electric field component in a direction (X-axis direction) perpendicular to the longitudinal direction of the wire grid is allowed to pass.
In addition, the pitch, line width/pitch, thin film height (thickness, lattice depth), and thin film length (lattice length) of the reflection layer 22 (thin film 22a) are preferably set in the following ranges.
The dielectric layers 23 are formed on the surface of the substrate 21 from an optical material, such as SiO2, transparent to visible light by a general vacuum film formation method, such as a sputtering method, a vapor phase growth method, or an evaporation method, or a sol-gel method (method for applying a sol by a spin coating method or the like, followed by thermal-curing to form a gel). The dielectric layer 23 is formed as an underlayer for the inorganic particle layer 25 and is also formed to have a thickness so as to shift the phase of a polarized light passing through the inorganic particle layer 25 and reflected by the reflection layer 22 by a half wavelength with respect to a polarized light reflected by the inorganic particle layer 25, which will be described later. In particular, the thickness may be appropriately set in the range of 1 to 500 nm. The dielectric layer 23 is preferably formed to enhance an interference effect by adjusting the phase of the polarized light and to have a thickness shifting the phase by a half wavelength. However, since the reflected light can be absorbed by the inorganic particle layer, which has an absorption effect, and improvement in contrast can be realized even if the film thickness is not optimized, the film thickness may be practically determined in consideration of desired polarization properties in combination with an actual manufacturing process. A practical film thickness is in the range of 1 to 500 nm.
As a material forming the dielectric layer 23, a general material, such as SiO2, Al2O3, or MgF2, may be used. These materials mentioned above may be formed into a thin film by a general vacuum film formation method, such as a sputtering method, a vapor phase growth method, or an evaporation method, or a method in which a sol material is applied on a substrate, followed by thermal-curing. In addition, the refractive index of the dielectric layer 23 is preferably set in the range of more than 1 to 2.5. Since the optical properties of the inorganic particle layer 25 are influenced by the refractive index of the surrounding material, polarizing element properties can also be controlled by the dielectric layer material.
The inorganic particle layer 25 is formed by adhering inorganic particles to the dielectric layer 23 at a position corresponding to that of the thin film 22a so that the inorganic particles are linearly disposed in one direction (absorption-axis Y direction) parallel with the primary surface of the substrate 21. In addition, since the inorganic particle layers 25 are formed above the respective thin films 22a regularly provided with predetermined intervals, the inorganic particle layers 25 form a stripe pattern, and hence the wire grid structure is formed.
In
As the optical constant of the inorganic particle layer 25 of this embodiment according to the present invention, the optical constant in the absorption-axis Y direction (disposed direction of the inorganic particles) is larger than that in the transmission-axis X direction (direction perpendicularly to the disposed direction of the inorganic particles). In particular, the refractive index of the inorganic particle layer 25 in the absorption-axis Y direction is larger than that in the transmission-axis X direction, and the extinction coefficient in the absorption-axis Y direction is larger than that in the transmission-axis X direction. In order to obtain the properties described above, the inorganic particle layers 25 are formed by an oblique sputtering method. The details of the oblique sputtering method are the same as those of the method shown in the first embodiment. In addition, a material for the inorganic particle layer 25 is the same as that for the inorganic particle layer 15 of the first embodiment.
In the polarizing element 20 thus formed of this embodiment, the front surface of the substrate 21, that is, the surface on which the strip-shaped thin films 22a, the dielectric layers 23, and the inorganic particle layers 25 are formed is used as a light incident surface. In addition, by using the following four functions, that is, the light transmission, reflection, interference, and selective light absorption of a polarized wave by optical anisotropic properties, the polarizing element 20 attenuates a polarized wave (TE wave (S wave)) having an electric field component (Y-axis direction) parallel with a wire grid longitudinal direction of the reflection layer 22 and transmits a polarized wave (TM wave (P wave)) having an electric field component (X-axis direction) perpendicular to the wire grid longitudinal direction.
That is, as shown in
The polarizing element 20 may be formed, for example, as described below. That is, after a metal film and a dielectric film are formed on the substrate 21, and a lattice pattern is formed by patterning the metal film and the dielectric film using a photolithographic technique or the like, the inorganic particle layers 25 are formed by an oblique sputtering deposition method. By adjusting an incident angle in the oblique sputtering deposition, particles can be intensively deposited in the vicinities of top parts of convex portions formed of the strip-shaped thin films 22a and the dielectric layers 23.
Besides the above method, a method may also be used in which a one-dimensional lattice pattern is formed on a transparent substrate using a transparent material, and metal layers, dielectric layers, and inorganic particle layers are sequentially formed on top parts of convex portions of this lattice pattern by oblique deposition. Furthermore, another method may also be used in which after a metal film, a dielectric film, and an inorganic particle film are sequentially formed on a substrate, these layers are simultaneously etched to form a one-dimensional lattice pattern.
Furthermore, as shown in
In addition, as the polarizing element of this embodiment according to the present invention, a polarizing element having the structure in which the dielectric layers 23 shown in
Next, as an emission-surface stray-light countermeasure (ghost countermeasure) for a liquid crystal projector, an example in which selective light absorption layers are provided on a rear surface side of the polarizing element 20 will be described.
In the polarizing element 20A of this embodiment, the reflection layers 22 having a one-dimensional lattice pattern are formed on a surface (one surface) of the substrate 21, and on the reflection layers 22, the dielectric layers 23 and the inorganic particle layers 25 are sequentially formed. In addition, on the rear surface (opposite side surface) of the substrate 21, selective light absorption layers 28 having optical anisotropic properties for a polarized wave are provided, each of which is composed of a convex portion 26 of a dielectric material and a second inorganic particle layer 27 formed on a top part or at least one of side surface parts of this convex portion 26.
In the polarizing element 20 which is not provided with the selective light absorption layers 28 having optical anisotropic properties for a polarized wave, since the rear surface of the substrate 21 has a mirror surface, return light, which passes through the polarizing element and is reflected by another optical element, such as a lens, disposed following the polarizing element, is again reflected by the above mirror surface. The stray light as described above causes degradation in image quality, such as ghost, in a liquid crystal projector.
In this embodiment, when the selective light absorption layers 28 having optical anisotropic properties for a polarized wave, having the above structure, are provided at the rear surface side of the substrate 21, the above stray light is absorbed, and reflection by the reflection layers 22 is prevented. The convex portions 26 forming the selective light absorption layers 28 having optical anisotropic properties for a polarized wave are formed from the same material as that for the dielectric layer 23 and are also formed into a one-dimensional lattice pattern extending in the same direction as that of the strip-shaped thin films 22a of the reflection layers 22. The second inorganic particle layer 27 is formed of inorganic particles linearly disposed on the top part or the side surface part of the convex portion 26 and is formed from a material similar to that for the inorganic particle layer 25 provided at the front surface side of the substrate 21, and hence the selective light absorption effect for incident light from the rear surface of the substrate 21 can be obtained.
As a method for forming the convex portions 26, as is the method for forming the dielectric layers 23, a sputtering method, a sol-gel method, or the like may be used. The formation of the convex shape is preferably formed by pattern processing using a photolithographic technique or press formation by a nanoinprinting method. As a method for forming the second inorganic particle layers 27, oblique deposition similar to that for the inorganic particle layers 25 provided at the front surface side of the substrate 21 is preferable. The second inorganic particle layer 27 is formed on the top part, one side surface part, or two side surfaces of the convex portion 26.
Alternatively, as another method for manufacturing the polarizing element 20A, by using the polarizing element 10 shown in
Next, as another ghost countermeasure for a liquid crystal projector, an example in which an antireflection layer is provided between the substrate 21 and the reflection layer 22 will be described.
The polarizing element 20B of this embodiment is formed for a purpose similar to that for the above polarizing element 20A. That is, in the polarizing element 20B of this embodiment, antireflection layers 29 are provided between the substrate 21 and the reflection layers 22. By the antireflection layers 29 provided under the reflection layers 22 having a one-dimensional lattice pattern, reflection of incident light from the rear surface of the substrate 21 is prevented.
As the antireflection layer 29, for example, a black layer, such as a carbon black layer, is preferably used. By the layer as described above, the incident light from the rear surface of the substrate 21 can be efficiently absorbed. In addition, besides carbons, an oxygen-deficient silicon oxide layer or a low reflection-material layer having a reflectance lower than that of the reflection layer 22 may also be used. Alternatively, a layer similar to the inorganic particle layer 25 may be used as the antireflection layer 29. In addition, in the example shown in the figure, in order to decrease the reflectance by obtaining an interference effect between the reflection layer 22 and the antireflection layer 29, a dielectric layer 2a is provided. The dielectric layers 2a and the antireflection layers 29, having a lattice pattern, can be simultaneously obtained when the reflection layers 22 are formed by patterning.
In addition, as another ghost countermeasure for a liquid crystal projector, the following method may also be used. That is, a rubbing treatment is performed on the surface of the substrate 21 so as to form a texture structure of irregularities in which fine streaks are aligned in one direction in accordance with the disposed direction of the inorganic particles 25a of the inorganic particle layers 25 which are subsequently formed on the above surface, and thin films (antireflection layers) of inorganic particles having shape anisotropic properties may then be formed by the above-described oblique sputtering method on the surface processed by the rubbing treatment in accordance with the disposed direction of the inorganic particles 25a. By the texture structure described above, the alignment properties of the inorganic particles are improved so that the long axis directions thereof are along the longitudinal directions of the fine streaks, and the polarization properties of the thin film are improved, so that the ghost countermeasure effect can be enhanced. In addition, an increase in transmission contrast properties as the polarizing element can also be expected.
As one variation of the second embodiment, at least one laminate structure of the dielectric layer 23 and the inorganic particle layer 25 may be further provided on the inorganic particle layer 25 to form a multilayer structure. An example of this multilayer structure is shown in
In a polarizing element 30 shown in
As a method for manufacturing the polarizing element 30 of this embodiment, the following three methods may be mentioned by way of example. That is, as a first method, after a reflection layer material (metal lattice material), and a dielectric film are laminated on the substrate 21, and a one-dimensional lattice pattern is formed, for example, by a nanoinprinting or a photolithographic technique using etching or the like, particles are deposited by an oblique sputtering deposition method. According to the above method, by adjusting an incident angle in the oblique sputtering deposition, inorganic particles can be intensively deposited in the vicinities of top parts of convex portions of the dielectric layers 23. In addition, as a second method, after a concave-convex member having a one-dimensional lattice pattern is formed on a transparent substrate using a transparent material, a reflection layer material, a dielectric layer material, and an inorganic particle material are sequentially and repeatedly deposited by oblique deposition in accordance with the number of laminates. In addition, as a third method, a laminate structure composed of a dielectric film and an inorganic particle thin film is repeatedly formed on a thin film (metal lattice film) for a reflection layer in accordance with the number of laminates, followed by etching. The inorganic particle material may have an imperfect island shape as long as it has a grain boundary. In addition, the dielectric layers 23 and the inorganic particle layers 25 may be formed by a method including sputtering deposition and etching in combination with a method using oblique sputtering deposition. When the above manufacturing processes are carried out, the type of substrate material is not particularly limited; however, when the substrate is used for a projector generating a large amount of heat, quartz or sapphire, having a high thermal conductivity, is preferably used.
Incidentally, in the polarizing element 30 having the structure as described above, since the light emission surface (reflection layer 22) is formed of a metal, when light returns, the reflectance is unfavorably increased. Accordingly, also in this embodiment, the emission-surface stray-light countermeasure described above is preferably used.
A polarizing element 30A is formed such that in the polarizing element 30, on the surface (rear surface) of the substrate 21 opposite to that on which the reflection layers 22 are formed, there are provided the selective light absorption layers 28 having optical anisotropic properties for a polarized wave, each of which is composed of the convex portion 26 of a dielectric material and the second inorganic particle layer 27 formed on the top part or at least one side surface part of the convex portion 26.
A polarizing element 30B is formed such that in the polarizing element 30, the antireflection layers 29 are provided under the reflection layers 22 having a one-dimensional lattice pattern, and the dielectric layers 2a are provided between the reflection layers 22 and the antireflection layers 29 in order to obtain the interference effect. In this embodiment, in
In the case in which the antireflection layer 29 and the dielectric layer 2a are provided under the reflection layer 22, or the antireflection layer 29 is directly formed under the reflection layer 22, when these films are formed before a film for the reflection layers is formed and are simultaneously etched when the reflection layers 22 are formed by etching, these layers can be formed only under the strip-shaped thin films 22a of the reflection layers 22, and hence it is possible not to give any influences on the transmission properties.
In addition, in the second embodiment, if desired, when the front and the rear surfaces of the substrate are coated with antireflection films, reflection at the interface between air and the substrate is prevented, and as a result, the transmission-axis transmittance can be improved. As the antireflection film, for example, there may be used a low refractive-index film of MgF2 or the like, which is generally used, or a multilayer film composed of a low refractive-index film and a high refractive-index film. In addition, after the structure shown in
Next, a liquid crystal projector of an embodiment will be described.
The liquid crystal projector of this embodiment according to the present invention has a lamp as a light source, a liquid crystal panel, and one of the polarizing elements 10, 20, 20A, 20B, 30, 30A, and 30B.
The engine portion of a liquid crystal projector 100 has an incident side polarizing element 10A, a liquid crystal panel 50, an emission pre-polarizing element 10B, and an emission main polarizing element 10C for red color LR; an incident side polarizing element 10A, a liquid crystal panel 50, an emission pre-polarizing element 10B, and an emission main polarizing element 10C for green color LG; an incident side polarizing element 10A, a liquid crystal panel 50, an emission pre-polarizing element 10B, and an emission main polarizing element 10C for blue color LB; and a cross dichroic prism which synthesizes the three types of light emitted from the individual emission main polarizing elements 10C and which emits the synthesized light to a projector lens. The polarizing elements 10, 20, and 30 of the embodiments are used as the incident side polarizing element 10A, the emission pre-polarizing element 10B, and the emission main polarizing element 10C, respectively.
In the liquid crystal projector 100 of this embodiment, after light emitted from a light source lamp (not shown) is separated into the red light LR, the green light LG, and the blue light LB by a dichroic mirror (not shown), these three types of light are injected into the respective incident side polarizing elements 10A, are then polarized thereby, and are further spatial-modulated by the respective liquid crystal panels 50, and these three types of light thus processed are then emitted therefrom. Subsequently, the red light LR, the green light LG, and the blue light LB thus emitted pass through the respective emission pre-polarizing elements 10B and emission main polarizing elements 10C, are then synthesized in the cross dichroic prism 60, and are subsequently emitted from the projector lens (not shown). Even when the light source lamp is a high power type, since the polarizing elements 10, 20, and 30 of the embodiments have superior light resistance against intense light, a highly reliable liquid crystal projector can be realized.
In addition, the polarizing elements of the embodiments are not limited to application for the liquid crystal projector and are preferably used as a polarizing element to be used in high temperature environments. For example, the polarizing elements of the embodiments according to the present invention may be used as a polarizing element for car navigation systems and/or liquid crystal displays.
Hereinafter, the verification results of polarization properties of the polarizing element of the embodiment will be described.
First, the optical properties of inorganic particle layers formed by the oblique sputtering deposition shown in
In
In addition, after the composition of the target 2 was changed from Ge to Si, a Si particle film was formed on the glass substrate 41 under the same conditions as those in the case of the Ge sputtering deposition, and the optical constants were measured. The results are shown in
Also in the case of Si, when sputtering deposition was performed in a 10° direction with respect to the surface of the glass substrate 41 (
Next, the polarization transmittance was obtained by simulation calculation in the case in which the Ge particle film 44 was formed to have a thickness of 20 nm on the glass substrate 41 under the conditions shown in
Next, influences of the optical anisotropic properties of the inorganic particle layer on a polarizing element were investigated. In particular, by using the polarizing elements having the structures shown in
According to the results shown in
In the polarizing element having a multilayer structure, polarization properties obtained when inorganic particle layers of Ge were formed by the method shown in
When the optical anisotropic properties were not present (data shown by dotted lines indicated as “isotropy”), as was the case of the single layer (
When inorganic particle layers having the optical anisotropic properties as described above are used for a polarizing element, the polarization properties can be improved. In addition, the optical constants of the inorganic particle layer preferably satisfy such that the transmission-axis direction optical constant is smaller than the absorption-axis direction optical constant, that is, it is important to satisfy the relationships in which the transmission-axis direction refractive index is smaller than the absorption-axis direction refractive index and in which the transmission-axis direction extinction coefficient is smaller than the absorption-axis direction extinction coefficient. Examples illustrating the above relationships are shown in
As was the case shown in
Next, the relationship between the optical anisotropic properties and the inorganic particles of the polarizing element of the embodiment according to the present invention was investigated.
(1) Inorganic Particle Layer on a Flat Plate
First, by using a substrate having a smooth and flat surface, which was a single crystal Si substrate provided with a SiO2 film having a thickness of 10 nm, a Ge particle film was formed under the same conditions as those in Example 1 (oblique sputtering deposition, and sputtering deposition in a direction perpendicular to the substrate surface), and the shape of Ge particles of the Ge particle film was observed by an atomic force microscope (hereinafter referred to as “AFM”). The results are shown in
In a sample obtained by oblique sputtering deposition, shown in
(2) Polarizing Element 10
Next, a sample of a polarizing element having the structure shown in
Analysis of the element distribution was performed for a cross-section of this polarizing element sample using a TEM, and it was found that as shown by element distribution mapping in
As shown in
In addition, an electron beam diffraction image of the Ge part in
(3) Polarizing Element 20
Next, a sample of a polarizing element having the structure shown in
The cross-section of this polarizing element sample was observed, and it was found that as shown in a schematic view shown in
In addition, in
The inorganic particle layers 25 were each formed from the top part to the sidewall part of the one-dimensional lattice dielectric layer 23 along the longitudinal direction thereof, and in addition, the inorganic particle layers 25 were each observed as a strip or a belt shape formed of the inorganic particles 25a which had shape anisotropic properties and were continuously disposed. In addition, each inorganic particle 25a was observed such that the long axis direction of the inorganic particle was the disposed direction and the short axis direction was perpendicular thereto.
From the above results, it is found that the inorganic particles of the polarizing element of the example according to the present invention have shape anisotropic properties by oblique sputtering deposition and are formed so that when the inorganic particles are disposed in a one-dimensional lattice pattern, the long axis directions of the inorganic particles are aligned in the lattice direction of the one-dimensional lattice. In addition, the inorganic particles are placed in an amorphous state. It is believed that in the present invention, the above-described properties of the inorganic particles relates to the expression of the optical anisotropic properties. The particles having shape anisotropic properties are formed by oblique sputtering deposition, and the expression of the shape anisotropic properties is called Steering Effect (Jikeun Seo, S.-M. Kwon, H.-Y. Kim, and J.-S. Kim, Phys. Rev. B67, 121402 (2003).
In addition, by oblique sputtering deposition, as shown in
In addition, although a thin film (such as a germanium thin film) having no optical anisotropic properties is formed on the dielectric layer 23 instead of the inorganic particle layer 25, when the thickness of the thin film is optimized, the reflectance in the absorption-axis direction can be suppressed. However, in this case, the reflection is suppressed dominantly by the interference effect, the wavelength band is narrow, and since absorption occurs in the transmission-axis direction, the transmission-axis transmittance is disadvantageously decreased. Furthermore, since the interference effect is sensitive to the thickness, in order to obtain desired properties, strict control of the thicknesses of the dielectric layer 23 and the germanium thin film are to be appropriately performed. On the other hand, in the present invention, since germanium particles having optical anisotropic properties are used, the degree of designing freedom is high, and also manufacturing can be easily performed.
Accordingly, by a rigorous coupling wave analysis (RCWA), the optical anisotropic properties of the inorganic particle layer 25 of the polarizing element 20 were simulated for two cases in which a thin film and fine particles were used for forming the inorganic particle layer 25 in order to obtain the difference therebetween. In this case, the reflection layer 22 was formed from Al to have a thickness of 200 nm, a lattice pitch of 150 nm, and an Al width of 45 nm, the dielectric layer 23 was formed from SiO2 to have a thickness of 30 nm. In addition, the dependences of the absorption-axis reflectance, the transmission-axis transmittance, and the transmission contrast on the thickness of the Ge thin film and the thickness of the Ge particle were calculated at a wavelength of 450 nm. In addition, as the optical constants of the Ge thin film, the values in
The results are shown in
Next, the relationship between the aspect ratio of the inorganic particle and the contrast of the polarizing element was investigated.
(1) Oblique Sputtering Deposition on a Flat Plate
First, Ge particle layers having a thickness of 30 nm were formed on a flat Si substrate at substrate inclined angles θ of 20° and 10° using the ion beam sputtering apparatus shown in
In addition, by using samples which included Ge particle layers having a thickness of 10 nm formed on a flat glass substrate (Corning 1737) at substrate inclined angles θ of 20° and 10° by the ion beam sputtering apparatus shown in
TABLE 1
Substrate
Ge particle
inclined angle
Transmittance (%)
Long axis
Aspect
θ (degree)
x direction
y direction
Contrast
length (nm)*
ratio*
20
63.2
72.4
1.1
30
3.2
10
58.4
74.9
1.3
63
4.0
*average value
(2) Polarizing Element 10
Polarizing element samples were formed under the same conditions as those for the polarizing element 10 of Example 5 except that the oblique sputtering deposition for forming the inorganic particle layers 15 were performed at substrate inclined angles θ of 10° and 20°. The transmittances of this sample in the transmission axis and the absorption axis were measured, and the transmittance ratio at a wavelength of 550 nm was obtained as the contrast. The results are shown in
TABLE 2
Substrate inclined angle
Transmittance (%)
θ (degree)
x direction
y direction
Contrast
20
88.3
37.2
2.4
10
90.7
33.9
2.7
As described above, although inorganic particles having shape anisotropic properties can be formed into films on the substrate by oblique sputtering deposition, the aspect ratio, which is a ratio between the major axis diameter and the minor axis diameter of the inorganic particle, depends on the incident angle (substrate inclined angle θ in
By changing the type of film formation method (dry process), Al particle layers were formed on the substrate. In this example, the following three dry processes were used.
(a) Electron Beam Deposition (
A substrate inclined by 10° with respect to the normal line direction of an evaporation source containing Al was set at a distance of 80 cm apart from the evaporation source, and electron beam deposition was performed at a film formation rate of 0.3 nm/sec.
(b) Magnetron Sputtering (
A substrate inclined by 10° with respect to the normal line direction of an Al target was set at a distance of 40 cm apart from the target, and magnetron sputtering deposition was performed at a film formation rate of 0.1 nm/sec.
(c) Ion Beam Sputtering (
The sputtering deposition method shown in
In this example, the same substrate as the substrate 11 of the polarizing element 10 of Example 5 was used and was set so that the Al incident direction was set along a direction (y direction) perpendicular to the lattice longitudinal direction (x direction) as shown in
The transmittances of the samples thus obtained were measured. The results are shown in
Among the three types of samples, since the sample obtained by the ion beam sputtering had a high transmittance, and the difference in transmittance in the x and y directions was large, it was found that ion beam sputtering was the most favorable film formation method.
Among the polarizing elements of the embodiments, in the polarizing element 20 having the structure shown in
In addition, in the polarizing element 20 having the structure shown in
TABLE 3
Dielectric
Absorption-axis reflectance
Transmission-axis
layer thickness
(%)
transmittance (%)
Contrast
(nm)
λ = 450 nm
λ = 550 nm
λ = 650 nm
λ = 450 nm
λ = 550 nm
λ = 650 nm
λ = 450 nm
λ = 550 nm
λ = 650 nm
0
19
18
26
72
82
86
1,800
2,929
3,440
19
8
3
3
72
83
86
3,130
3,952
4,315
37
3
2
2
78
84
86
2,167
3,652
3,913
56
11
10
8
75
83
85
1,875
3,773
4,739
74
30
22
21
73
85
86
1,460
4,250
5,369
From the results thus obtained, for example, when it is desired to decrease the absorption-axis reflectance, the thickness of the dielectric layer 23 may be set in the range of 19 to 37 nm. In addition, when the polarizing element is used for application in which reflection may not cause any serious problems, the thickness of the dielectric layer 23 may be decreased to zero. This means a decrease in number of manufacturing steps, and hence the productivity can be improved. In addition, since a high contrast is realized at a wavelength in the range of 450 to 650 nm, the polarizing element can be preferably applied to a projector used in a wide service bandwidth.
On the other hand, as for the transmittance, a high transmittance is realized such as 70% or more at a wavelength of 450 nm and 80% or more at wavelengths of 550 and 650 nm. When the pitch of the lattice is further decreased, the transmittance can be further improved.
In addition, the contrast can be adjusted by the height of the metal lattice. When a higher contrast is preferable, the height of an Al lattice may be increased, and when a lower contrast is preferable, the height may be decreased.
Next, in
In the polarizing elements of the example according to an embodiment, when the lattice shape (the shapes and heights of the convex portions 14a in
In the polarizing element 20 shown in
In this example, by using D20000 manufactured by Nihon Micro Coating Co., Ltd. as a polishing material, the effect described above was verified. Corning 1737 glass was used as the substrate, and the texture was formed by rubbing the surface of the substrate in one direction with D20000. The substrate surface after the texture was formed was measured by an AFM, and the measurement result is shown in
Subsequently, by using the ion beam sputtering apparatus shown in
In
According to an embodiment, the example sample (the textured substrate provided with the antireflection film formed thereon) is used, and the layered structure of the polarizing element 20 shown in
According to the above examples, in the most cases, the polarizing elements were described using Ge by way of example; however, inorganic particles having shape anisotropic properties can be formed using another material. Hence, by appropriately selecting a material, a polarizing element to be used at a targeted wavelength can be formed.
It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
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